In recent years, with an improvement in areal recording density of magnetic recording media to meet a demand for increase in recording capacity of hard disk drives (HDDs), the size of each writing bit on the magnetic recording media has become extremely small, i.e., about several 10 nm. Even when each writing bit has such an extremely small size, there is a demand for improvement in an S/N ratio while reducing a ratio of noise components contained in a read signal upon reading of information written on the magnetic recording media.